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effect in four of these ten reservoirs. As expected. the suppression heat is the dominant secondary effect in large reservoirs such as Bear Lake, lake Powell. and Flaming Gorgc which have relatively low outflow to total storage ratios. Natural lakes Bear Lake is the only impoundment in this group which does not have an out lei below lhe thermocline. The flow from Bear Lake is essentially from the surface. and monthly surface rather than bottom temperatures were used for the outlet heat change calculation. This results in outlet flows causing a negative rather than a positive effect on suppression for Bear Lake. This effect can be observed by the 'I, ratio between idealized and final suppression estimates (the lowest of any reservoir) and the high residual temperature (almost equal to Lake Powell even though suppression is much less). If the 24-month model were applied to Bear Lake the total May to October suppression would be completely balanced by the negative winter and spring suppression. In fact. the net effect would be negative because of the less than normal heat loss from the outlet. The obvious conclusion is that natural lakes (or man-made reservoirs which have their outlet above the thermocline) should never be destratified for purposes of evaporation suppression. Residual heat The seasonal residual heat is a good indicator of the magnitude of probable negative suppression during later months. This is [he net increase in average temperature of the reservoir due to the destratification. Of the ten reservoirs in the sample only lwo of them have residual temperatures greater than IOC. This implies that although some above normal evaporation will occur in the other eight impoundments during the winter, its magnitude should be quite small. A better indication of this magnitude can be obtained from the 24-month model discussed later. Flaming Gorge residual heat is only IOC even though it has a large carryover storage and little draw down. This demonstrates that the positive effect of outlet heat is not necessarily a draw down effect. Flaming Gorge outflow is almost balanced by inflow even during the summer and the outflow/storage ralio is essentially independent of draw down. This implies that even with a large year to year carryover storage the annual net suppres- sion for Flaming Gorge would not be much less than the May to October model suppression. The high residual heat for Bear Lake has already been discussed. The Lake Powell residual heat will be discussed in connection with the 24 month model. Twenty-four Month Model The only reservoir for which winter tempera- lure profile data were available is Lake Powell. The mode' was applied 103 years of Lake Powell data as described previously. The detailed outpul for various startup months is given in Appendix H. Figure 14 displays the variation of suppression with initial date for which mixing is achieved. Optimum suppression rates for both the initial calendar year and after residual heat has decayed are achieved by initial mixing during April. Mixing during March would achieve essentially the same amount of water salvage but al a higher operating cost (longer period). The monthly values of the important para- meters for April I start up and historic draw down are given in Table 3. The monthly suppression varies from 44 percent in June to -16 percent during the following January. The maximum decrease in surface temperature is 9.JoC which occurs in July and the maximum residual heat added to the reservoir is 3.60C which occurs in September. The suppression at the end of the first season of mixing is 27.3 percent but lhe residual heat ultimately reduces this to a net suppression of22.5 percent for the first year. The suppression expected during several consecutive years of operation can be determined by running the model several times with the residual heat (TSUMB) from the previous year input as initial added heat (TPREV) for lhe current year. Appendix H gives the model output for four such consecutive years. These results are summar- ized in Table 4. Continuous operation results in a fairly rapid convergence (3 years) to residual heat of 2.90C which gives a continuous annual suppression of22.3 percent. A penalty of 6 percent (36,000 ac ft) however, is incurred during the season following the stop of mixing operations. The long term quantity of salvageable water for a draw down averaging 86 feet below capacity is estimated to be 140.200 acre feet. This would increase with higher reservoir levels. Maldple Regresllon Model The results of the 6-month model application to 10 Utah reservoirs (see Table 2) were used in a multiple regression analysis to develop a model for estimating suppression on reservoirs for which 34